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<meta name="description" content="动机1.在某些情况下，我们可能会“过度地使用继承来扩展对象的功能”，由于继承为类型引入的静态特质，使得这种扩展方式缺乏灵活性；并且随着子类的增多（扩展功能的增多），各种子类的组合（扩展功能的组合）会导致更多子类的膨胀。 2.如何使“对象功能的扩展”能够根据需要来动态地实现？同时避免“扩展功能的增多”带来的子类膨胀问题？从而使得任何“功能扩展变化”所导致的影响降为最低？">
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<meta property="og:description" content="动机1.在某些情况下，我们可能会“过度地使用继承来扩展对象的功能”，由于继承为类型引入的静态特质，使得这种扩展方式缺乏灵活性；并且随着子类的增多（扩展功能的增多），各种子类的组合（扩展功能的组合）会导致更多子类的膨胀。 2.如何使“对象功能的扩展”能够根据需要来动态地实现？同时避免“扩展功能的增多”带来的子类膨胀问题？从而使得任何“功能扩展变化”所导致的影响降为最低？">
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<meta name="twitter:description" content="动机1.在某些情况下，我们可能会“过度地使用继承来扩展对象的功能”，由于继承为类型引入的静态特质，使得这种扩展方式缺乏灵活性；并且随着子类的增多（扩展功能的增多），各种子类的组合（扩展功能的组合）会导致更多子类的膨胀。 2.如何使“对象功能的扩展”能够根据需要来动态地实现？同时避免“扩展功能的增多”带来的子类膨胀问题？从而使得任何“功能扩展变化”所导致的影响降为最低？">
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        <h1 id="动机"><a href="#动机" class="headerlink" title="动机"></a>动机</h1><p>1.在某些情况下，我们可能会“过度地使用继承来扩展对象的功能”，由于继承为类型引入的静态特质，使得这种扩展方式缺乏灵活性；并且随着子类的增多（扩展功能的增多），各种子类的组合（扩展功能的组合）会导致更多子类的膨胀。</p>
<p>2.如何使“对象功能的扩展”能够根据需要来动态地实现？同时避免“扩展功能的增多”带来的子类膨胀问题？从而使得任何“功能扩展变化”所导致的影响降为最低？</p>
<a id="more"></a>
<hr>
<h1 id="模式定义"><a href="#模式定义" class="headerlink" title="模式定义"></a>模式定义</h1><p>动态（组合）地给一个对象增加一些额外的职责。就增加功能而言，Decorator模式比生成子类（继承）更为灵活（消除重复代码&amp;减少子类个数）。</p>
<p>​                                                                                                       –《设计模式》GoF</p>
<hr>
<h1 id="结构"><a href="#结构" class="headerlink" title="结构"></a>结构</h1><p><img src="/2019/06/21/designpatterndecorator/decorator.png" alt="装配模式"></p>
<hr>
<h1 id="代码示例"><a href="#代码示例" class="headerlink" title="代码示例"></a>代码示例</h1><p>我们实现一个流功能，基本的有文件流、网络流、内存流，功能性的有加密流、Buffer流、加密Buffer流等。</p>
<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br><span class="line">185</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//业务操作</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Stream</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">    <span class="keyword">public</span>： <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span> </span>= <span class="number">0</span>;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span> </span>= <span class="number">0</span>;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span> </span>= <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">virtual</span> ~Stream() &#123;&#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//主体类</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">FileStream</span> :</span> <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//读文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//定位文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//写文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">NetworkStream</span> :</span> <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//读网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//定位网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//写网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">MemoryStream</span> :</span> <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//读内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//定位内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//写内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//扩展操作</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CryptoFileStream</span> :</span> <span class="keyword">public</span> FileStream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        FileStream::Read(number); <span class="comment">//读文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        FileStream::Seek(position); <span class="comment">//定位文件流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(byte data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        FileStream::Write(data); <span class="comment">//写文件流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CryptoNetworkStream</span> :</span> : <span class="keyword">public</span> NetworkStream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        NetworkStream::Read(number); <span class="comment">//读网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        NetworkStream::Seek(position); <span class="comment">//定位网络流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(byte data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        NetworkStream::Write(data); <span class="comment">//写网络流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CryptoMemoryStream</span> :</span> <span class="keyword">public</span> MemoryStream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        MemoryStream::Read(number); <span class="comment">//读内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        MemoryStream::Seek(position); <span class="comment">//定位内存流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(byte data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        MemoryStream::Write(data); <span class="comment">//写内存流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">BufferedFileStream</span> :</span> <span class="keyword">public</span> FileStream</span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">BufferedNetworkStream</span> :</span> <span class="keyword">public</span> NetworkStream</span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">BufferedMemoryStream</span> :</span> <span class="keyword">public</span> MemoryStream</span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CryptoBufferedFileStream</span> :</span> <span class="keyword">public</span> FileStream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        <span class="comment">//额外的缓冲操作...</span></span><br><span class="line">        FileStream::Read(number); <span class="comment">//读文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        <span class="comment">//额外的缓冲操作...</span></span><br><span class="line">        FileStream::Seek(position); <span class="comment">//定位文件流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        <span class="comment">//额外的缓冲操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(byte data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        <span class="comment">//额外的缓冲操作...</span></span><br><span class="line">        FileStream::Write(data); <span class="comment">//写文件流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        <span class="comment">//额外的缓冲操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">Process</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//运行时装配</span></span><br><span class="line">    CryptoFileStream *fs1 = <span class="keyword">new</span> CryptoFileStream();</span><br><span class="line"></span><br><span class="line">    BufferedFileStream *fs2 = <span class="keyword">new</span> BufferedFileStream();</span><br><span class="line"></span><br><span class="line">    CryptoBufferedFileStream *fs3 = <span class="keyword">new</span> CryptoBufferedFileStream();</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>上述实现的代码，会引入一个问题–当需要添加新的功能流时，变化非常多，我们应该将每一个功能流实现一个职责，而不是通过组合的方式实现不同流的功能，将这种静态组合变为动态组合。</p>
<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//业务操作</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Stream</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span>： <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span> </span>= <span class="number">0</span>;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span> </span>= <span class="number">0</span>;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span> </span>= <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">virtual</span> ~Stream() &#123;&#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//主体类</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">FileStream</span> :</span> <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//读文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//定位文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//写文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">NetworkStream</span> :</span> <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//读网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//定位网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//写网络流</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">MemoryStream</span> :</span> <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//读内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//定位内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(<span class="keyword">char</span> data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//写内存流</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//扩展操作</span></span><br><span class="line"></span><br><span class="line">DecoratorStream : <span class="keyword">public</span> Stream</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">protected</span>:</span><br><span class="line">    Stream *stream; <span class="comment">//...</span></span><br><span class="line"></span><br><span class="line">    DecoratorStream(Stream * stm) : stream(stm)</span><br><span class="line">    &#123;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CryptoStream</span> :</span> <span class="keyword">public</span> DecoratorStream</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    CryptoStream(Stream *stm) : DecoratorStream(stm)</span><br><span class="line">    &#123;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">char</span> <span class="title">Read</span><span class="params">(<span class="keyword">int</span> number)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        stream-&gt;Read(number); <span class="comment">//读文件流</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Seek</span><span class="params">(<span class="keyword">int</span> position)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        stream::Seek(position); <span class="comment">//定位文件流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">Write</span><span class="params">(byte data)</span></span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">        stream::Write(data); <span class="comment">//写文件流</span></span><br><span class="line">        <span class="comment">//额外的加密操作...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">BufferedStream</span> :</span> <span class="keyword">public</span> DecoratorStream</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line">    Stream *stream; <span class="comment">//...</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    BufferedStream(Stream *stm) : DecoratorStream(stm)</span><br><span class="line">    &#123;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">Process</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//运行时装配</span></span><br><span class="line">    FileStream *s1 = <span class="keyword">new</span> FileStream();</span><br><span class="line"></span><br><span class="line">    CryptoStream *s2 = <span class="keyword">new</span> CryptoStream(s1);</span><br><span class="line"></span><br><span class="line">    BufferedStream *s3 = <span class="keyword">new</span> BufferedStream(s1);</span><br><span class="line"></span><br><span class="line">    BufferedStream *s4 = <span class="keyword">new</span> BufferedStream(s2);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<hr>
<h1 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h1><p>1.通过采用组合而非继承的手法，Decorator模式实现了在运行时动态扩展对象功能的能力，而且可以根据需要扩展多个功能。避免了使用继承带来的“灵活性差”和“多子类衍生问题”。</p>
<p>2.Decorator类在接口上表现为is-a Component的继承关系，即Decorator类继承了Component类所具有的接口。但是在实现上又表现为has-a Component的组合关系，即Decorator类又使用了另一个Component类。</p>
<p>3.Decorator模式的目的并非解决“多子类衍生的多继承”的问题，Decorator模式应用的要点在于解决“主体类在多个方向上的扩展功能”——是为“装饰”的含义。</p>

      
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#动机"><span class="nav-number">1.</span> <span class="nav-text">动机</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#模式定义"><span class="nav-number">2.</span> <span class="nav-text">模式定义</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#结构"><span class="nav-number">3.</span> <span class="nav-text">结构</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#代码示例"><span class="nav-number">4.</span> <span class="nav-text">代码示例</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#总结"><span class="nav-number">5.</span> <span class="nav-text">总结</span></a></li></ol></div>
            

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